Semiconductor films, such as silicon films, are known to be used for providing pixels for liquid crystal display devices. Such films have previously been processed (i.e., irradiated by an excimer laser and then crystallized) via excimer laser annealing (“ELA”) techniques. However, the semiconductor films processed using such known ELA methods often suffer from microstructural non-uniformities such as edge effects, which manifest themselves in availing a non-uniform performance of thin-film transistor (“TFT”) devices fabricated on such films. In addition, it may take approximately 200 second to 600 seconds to completely process the semiconductor film sample using the ELA techniques, without even taking into consideration the time it takes to load and unload such sample.
Other more advantageous processes and systems for processing the semiconductor thin films for use in the liquid crystal displays and organic light emitting diode displays for fabricating large grained single crystal or polycrystalline silicon thin films using sequential lateral solidification (“SLS”) techniques have been described. For example, U.S. Pat. Nos. 6,322,625 and 6,368,945 issued to Dr. James Im, and U.S. patent application Ser. Nos. 09/390,535 and 09/390,537, the entire disclosures of which are incorporated herein by reference, and which are assigned to the common assignee of the present application, describe such SLS systems and processes. These patent documents describe certain techniques in which one or more areas on the semiconductor thin film are, e.g., sequentially irradiated. One of the benefits of these SLS techniques is that the semiconductor film sample and/or sections thereof can be processed (e.g., crystallized) much faster that it would take for the processing the semiconductor film by the conventional ELA techniques. Typically, the processing/crystallization time of the semiconductor film sample depends on the type of the substrates, as well as other factors. For example, it is possible to completely process/crystallize the semiconductor film using the SLS techniques in approximately 50 to 100 seconds not considering the loading and unloading times of such samples.
In order to uniformly process the semiconductor films, it is important for the beam pulse to be stable. Thus, to achieve the optimal stability, it is preferable to pulse or fire the beam constantly, i.e., without stopping the pulsing of the beam. Such stability may be reduced or compromised when the pulsed beams are turned off or shut down, and then restarted. However, when the semiconductor sample is loaded and/or unloaded from a stage, the pulsed beam would be turned off, and then turned back on when the semiconductor sample to be processed was positioned at the designated location on the stage. The time for loading and unloading is generally referred to as a “transfer time.” The transfer time for unloading the processed sample from the stage, and then loading another to-be-processed sample on the stage is generally the same when for the ELA techniques and the SLS techniques. Such transfer time can be between 50 and 100 seconds.
In addition, the costs associated with processing semiconductor samples are generally correlated with the number of pulses emitted by the beam source. In this manner, a “price per shot/pulse” is established. If the beam source is not shut down (i.e., still emit the beam pulses) when the next semiconductor sample is loaded unto the stage, or unloaded from the stage, the number of such irradiations by the beam source when the sample is not being irradiated by the beam pulse and corresponding time therefore is also taken into consideration for determining the price per shot. For example, when utilizing the SLS techniques, the time of the irradiation, solidification and crystallization of the semiconductor sample is relatively short as compared to the sample processing time using the ELA techniques. In such case, approximately half of the beam pulses are not directed at the sample since such samples are being either loaded into the stage or unloaded from the stage. Therefore, the beam pulses that are not impinging the samples are wasted.
Another exemplary technique for processing semiconductor thin film has been developed. In particular, such system and process can produce generally uniform areas on the substrate films such that the TFT devices can be situated in such areas. For example, portions of the irradiated film are irradiated, then nucleated (based on the threshold behavior of the beam pulse), and then solidified, such that upon re-solidification, the nucleated area becomes a region with uniform small grained material (to be referred to herein below as the “UGS techniques”). Thus, such UGS techniques are different from the SLS techniques in that for the SLS-techniques, the nucleated areas are avoided, while for the UGS techniques, the nucleated areas are utilized for placing the TFT devices therein. Indeed, using the UGS technique, there can be significant time savings since each irradiated area of the semiconductor thin film is irradiated once, without the need to re-irradiate a substantial portion thereof, while still providing a good uniform material therein. Many of these UGS techniques are described in U.S. Patent Application Serial Nos. 60/405,084, 60/405,083 and 60/405,085, and International Applications PCT/US03/25946, PCT/US03/25972 and PCT/US03/25954, the entire disclosures of which are incorporated herein by reference.
Accordingly, it is preferable to reduce the price per shot, without stopping the emission of the beam pulses. It is also preferable to be able to process two or more semiconductor samples, without the need to stop or delay the emission of the pulsed beam by the beam source until the samples are loaded on the respective stages.